It's already added: when a player has invisible armor in the body slot, their name tag simply won't be drawn (I tested it). There is no way to avoid the code being entirely client side (able to be modded out of the txt files), short of some very complicated hacking of the game engine, like the WSE. I don't think anybody needs to worry about it getting modded though, as hardly anybody would want to, and of those few, even less would know how. I probably just confused people by mentioning what would be possible with txt file hacks...